The long-term objective is to understand the sequence of neuronal events along the visual pathways involved in pattern recognition. Such knowledge about normal visual function may help in understanding and perhaps subsequently ameliorating both congenital and acquired disorders of higher visual function. The specific aim is a systematic study to examine the non-linear spatiotemporal filtering performed by complex and complex-like cells in primate visual areas V1, V2, V3 and V4. The method used to derive a quantitative estimate of the linear and 2nd-order nonlinear interaction volumes is the reverse correlation technique of DeBoer and Kuyper (1968). In each cortex studied, microlesions will be made at key recording sites which, in turn, will be referred to cytochrome oxidase, Nissl and myelin staining patterns. Three types of experiments will be performed in V1 and V2. First, the linear and 2nd-order nonlinear interaction components in the response of neurons to paired, localized stimuli that simultaneously differ in luminosity and/or chromaticity, 2-D spatial position and time of presentation will be examined. Examination of 2-D spatial interactions will permit quantitative assessment of such phenomena as end-stop inhibition, curvature sensitivity, and subfield skew. Second, the temporal dynamics of linear and non-linear cross-orientation and cross-frequency interactions will be studied with achromatic gratings which differ in their 2-D spatial-frequency and time of presentation. Third, linear and non-linear interaction results will be obtained for achromatic stimuli that are presented binocularly in order to gain further information on how the separate right and left eye inputs interact over space and time. These same three types of studies will be performed in V3 and V4 with additional attention to the following issues. Neurons in V3 antagonistically combine spatially localized mechanisms which are themselves non-linear and selective for spatial frequency. Investigation is proposed to determine how V3 neurons combine these postulated nonlinear mechanisms. Cells in V4 may nonlinearly combine information across stimulus dimensions that include orientation, spatial frequency and perhaps phase. In order to understand how such information might be processed, a study will be made of the linear and low-order nonlinear response properties of V4 cells to the stimuli described above.